Osteoporosis and other degenerative bone diseases have a serious impact on the health of elderly individuals. This laboratory has recenfly characterized a number of age-related changes in purified human bone precursor cells obtained from human bone marrow. Based on the hypothesis that age-related changes in this cell population are associated with changes in an obligate interaction with a bone- accessory cell population, this project will investigate: a) the phenotype of the bone-accessory cell population; b) the functional significance of these cells; and c) the age-related changes that take place in the bone-accessory cell population. This study will provide a better understanding of the mechanism of growth regulation in the osteoblast lineage, and will provide a foundation for improvement of future treatments for degenerative bone diseases.